Hello, If this is not a right place to ask this question, please tell me another place to ask. I'm developing a mail server with GHC 6.10.3 on Linux. The server is running well at the beginning. But after several hours, it receives an error, "buildFdSets: file descriptor out of range". Please tell me what happened? And please suggest me how to fix this problem. Here is brief description of the server. - linked with ADNS. - complied with the -threaded option since ADNS requires it. - uses forkIO to produce threads. - does not use "deamonize" of System.Posix.Daemonize since it uses forkProcess. I execute my server as foreground process. - Because there are so many nasty SMTP clients, most SMTP connections are time out. Handles of the SMTP connections disappear, so I cannot use "hClose" to close the handles. - pushes the limit of file descriptors to 65536 with setResourceLimit. --Kazu